In recent years, because of its energy-saving property and long life, a light emitting device using a Light Emitting Diode (LED) as a light source has been prevalent in a wide range of fields. An LED element is fixed to a copper alloy lead frame having excellent thermal and electrical conductivities and embedded in a package. To efficiently retrieve light emitted from the LED element, an Ag plating coating is formed as a reflective film on the surface of the copper alloy lead frame. As a copper alloy for a lead frame for LED, C194 having a strength of about 450 N/mm2 and an electrical conductivity of about 70% IACS is frequently used (see Patent Documents 1 and 2).
To enhance the brightness of an LED package, there are a method which enhances the brightness of an LED element and a method which increases the quality (reflectance) of Ag plating. However, the brightness of the LED element has been enhanced almost to the limit and only a slight increase in brightness results in a significant increase in element cost. As a result, in recent years, there has been strong demand for the increased reflectance of the Ag plating.
On the other hand, under the great influence of the surface state of a copper alloy raw material, the Ag plating is likely to develop a defect which inhibits the reflection property of the Ag plating, such as a projection, non-deposition, or a streaky pattern. In particular, the C194 used frequently for a copper alloy lead frame for LED contains Fe, Fe—P, or Fe—P—O grains in the raw material thereof so that these grains exposed at the surface thereof cause the Ag plating defect mentioned above, which degrades the reflectance of the Ag plating.
In addition, a high-brightness LED used mainly for illumination emits a large amount of heat against all expectations and the emitted heat may degrade the LED element or the resin therearound and impair a long life, which is an advantageous feature of the LED. Accordingly, measures against heat dissipated from the LED are considered to be important. As one of the measures against the heat dissipation, an LED lead frame having an electrical conductivity (thermal conductivity) higher than that of the C194 mentioned above has been in demand.